The present invention relates generally to the formation of integrated circuit devices and structures, and more specifically to a technique for filling plugs through chemical mechanical polishing.
Silver and other malleable metals including gold, platinum, and copper are considered important materials for manufacturing a variety of integrated circuits such as memory devices. For example, aluminum is a commonly used metal for forming devices and interconnects.
Unfortunately, there are a number of manufacturing obstacles attributable to the use of such materials in integrated circuit device fabrication. For example, one common processing technique, chemical mechanical polishing (CMP), is commonly employed in integrated circuit device fabrication for polishing away conductive materials for forming plugs, interconnects and other devices. However, it is not uncommon for certain malleable metals such as silver and silver-based materials to inadvertently pull from the plug during CMP processing. This is particularly problematic when forming devices and interconnects where silver is intended to form a plug coupling to an underlying layer of tungsten. Silver adheres poorly to tungsten, thus the silver pulls easily from the plug. Even in cases where the metal does not completely pull from the via, inconsistent or otherwise unreliable structures such as partially filled vias can result post CMP. This can lead to open circuit connections or high resistance plugs.
Therefore, there is a continuing need for a CMP process in integrated circuit device fabrication that allows consistent and reliable formation of devices and interconnects using malleable metals.
This need is met by the present invention wherein a scheme for filling plugs comprises depositing a malleable conductive layer over a dielectric layer having openings formed therein. The malleable conductive layer is deposited such that a liner is formed within the openings, however the openings are not completely filled. A chemical-mechanical polishing (CMP) process is then performed such that the malleable conductive layer smears, filling the openings and defining filled or substantially filled plugs.
More specifically, a special chemical mechanical polishing (CMP) process is used to fill the remainder of the vias with the malleable conductive layer such that reliable devices and interconnects are formed. For example, when using a silver-based conductive material as the malleable conductive layer, the silver-based conductive material is polished by CMP using an alumina based slurry at a neutral or slightly basic pH and no oxidizer. It is believed that at least a portion of the silver-based conductive material smears sufficiently during the CMP process to fill the remainder of the vias, forming filled or substantially filled plugs. It will be appreciated that the slurry composition will vary depending upon the malleable metal used for the CMP.